Unlike traditional cameras that use films to capture and store images, today's digital cameras use solid-state image sensors to acquire images. Such image sensors are typically disposed on fingernail-sized silicon chips containing millions of photoelectric devices such as photodiodes arranged in an array of pixels. During exposure, each photoelectric device records intensity or brightness of an incident light by converting optical energy into accumulated electrical charges. The brightness recorded by each photoelectric device can then be read out and stored as digital signals.
One problem associated with solid-state image sensors is their limited dynamic range. Dynamic range is the ratio of maximum and minimum light intensities that an image sensor can capture. The charge holding capacity of each photoelectric device in the image sensor typically determines its dynamic range. Thus, the limited capacity of each photoelectric device limits the image sensor's ability to capture bright and dark subjects at the same time. As a result, if a long exposure is used to capture dark subjects, bright subjects can lose contrast and become a bright spot. If a short exposure is used to capture bright subjects, dark subjects can blend into a dark background and simply disappear.
Another problem associated with solid-state image sensors is blooming. Blooming occurs when a photoelectric device of the image sensor overflows and spills accumulated charges (e.g., electrons) into neighboring photoelectric devices. The spilled charges can distort the brightness recorded by the neighboring photoelectric devices and ultimately reduce spatial resolution. For example, the brightness recorded by a neighboring photoelectric device can be falsely high due to the spilled charges. As a result, the bright subjects causing blooming often appear to have a “glow” around them in a captured image.